(1) Field of the Invention
The present invention relates to an air intake grid and in particular to an air intake in an aircraft power plant, the aircraft having a rotary wing, for example.
The technical field of the invention is more particularly restricted to the field of combating icing on air intake grids.
(2) Description of Related Art
Since rotorcraft need to operate in a variety of environments, including under extreme conditions, the turboshaft engine(s) of such a rotorcraft needs to be protected so as to withstand such conditions.
To feed a rotorcraft turboshaft engine with air, the engine has an air intake, and the air intake is provided with a duct connecting the engine to the outside air. Two types of air intake can be distinguished, namely:
a dynamic air intake that is fed with outside air under the effect firstly of the forward speed of the aircraft and secondly of the suction drawn in by the engine; and
a static air intake that is fed with air solely under the effect of the suction drawn in by the engine.
In order to avoid the engine ingesting solid bodies that might damage it, e.g. birds, it is common practice to protect an air intake with a grid. Said solid bodies are then blocked by the grid and do not run the risk of penetrating into the engine.
Although effective, that solution presents a drawback under so-called “icing” flying conditions, and this applies more particularly with dynamic air intakes. Under such flying conditions, ice becomes deposited on the grid and closes off the interstices in the grid, partially, or even totally.
Consequently, the air intake becomes partially, or even totally, closed. The supply of air to the engine is thus reduced, or even eliminated, thereby giving rise to a significant, or even a complete, drop in the power developed by said engine, which could lead to an incident.
To remedy that, it is possible to envisage using an oversized grid. For a dynamic air intake having an area through which air penetrates dynamically into the dynamic air intake, the protective grid has first and second air-passing sections, with the first air-passing section facing the air-passing area, in contrast to the second air-passing section that does not face said area. The grid can be said to be somewhat like a mushroom cap covering the dynamic air intake.
Thus, only the first air-passing section runs the risk of picking up ice. Under icing conditions, the second air-passing section continues to guarantee at least some minimum air flow rate.
It should be observed that aircraft manufacturers have thus devised a variety of devices for protecting the air intake of turboshaft engines so as to prevent particles of all kinds being ingested by such engines. For example, document FR 2 250 671 discloses a multipurpose air intake capable both of preventing the turboshaft engine from ingesting particles and of allowing flight to take place under icing conditions, without suffering significant loss of performance from the engine.
Document U.S. Pat. No. 4,393,650 is remote from the invention since it relates to a gas turbine having a pointed rotating fairing as opposed to a stationary grid. That rotating fairing has a rigid conical end followed by a rotating flexible frustoconical portion for breaking the plates of ice that become deposited on the fairing.
Similarly, document GB 663 194 describes a rotary screen provided with wires that are elongate in a radial direction, said screen co-operating with an annular groove that is drained by pipework.
Thus, ice that is deposited on the wires is expelled towards the groove and then evacuated by the pipework. It is also possible to inject a de-icing fluid onto the wires.
Document U.S. Pat. No. 5,411,224 describes a grid provided with a front portion and a rear portion, the rear portion having pointed rigid elements for breaking up foreign bodies that might pass through the grid.